This is the locating bolt for the cross-shaft bushing.
We offer it in two lengths, 14mm for the OEM bell housing,and a longer 18mm length for the late-style aluminum bell housings. The additional length on the 18mm bolt provides more thread engagement, which means it is less likely to strip out. We call that an upgrade!
Fit note: 18mm fits new aluminum late-style 091-301-071E bell housing only.